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  • hudnut
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Thanks Jeff, it was good to re-read this paper. The time evolution of those sequences is very interesting and nicely explained in this paper. So, I wonder what will happen next (if anything)?
  • jmcguire
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Here's Rowena Lohman and my's recent JGR paper on the 2005 and 1981 swarms further south.
  • jmcguire
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Here's a figure we use to decide if a swarm is likely the result of a fault creep event. It compares the shape of the moment-rate history (measured as skewness) versus the stress drop. Swarms that appear to be associated with creep events have small or negative skews and low stress drops, whereas ordinary aftershock sequences tend to have positive skews and stress drops in the 1-10 MPa range (this is the total moment of the sequence scaled by a rough estimate of the total seismogenic area of the fault). The recent Bombay Beach swarm looks a lot like other Salton Trough and EPR swarms, including the 2005 Obsidian Buttes swarm a little to the south that had a lot of shallow creep associated with it. -Emily Roland updated the plot this morning with clearer labels, etc.
  • hudnut
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    The "ladder" structure in the northern Brawley Seismic Zone (BSZ) has become more evident since 1989, partly through activity of the fine structures and also through precise re-locations by Lin, Shearer and Hauksson. Also, through on-land mapping by Susanne Janecke and her group, and also off-shore mapping in the Salton Sea by Danny Brothers, Neil Driscoll and Graham Kent at Scripps, the structures of the Extra fault zone have been much better mapped. It seems that the activity up through this time is confined to the "ladder" structure, and has not broken out onto the major NE-oriented block edge boundary that is the main Extra fault zone. There was some increased activity beginning around April 1987 near the junction of the BSZ and the projection of the Elmore Ranch fault zone. I don't imagine that we should expect things to exactly mirror what happened back in 1987, but I do think that becoming familiar again with some details of the 1987 sequence might help with understanding the current sequence better. Thanks to Ramon for posting these several papers, and I've taken the liberty of adding our 1989 GRL paper as well, since it makes the leap to discussing cross-fault triggering in the sense that is most directly applicable to the current situation with the latest Bombay Beach sequence.
  • hudnut
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    This latest event seems to be on the same "ladder rung" that was active earlier today.
  • hudnut
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Today the locus of activity moved to the southeast. The largest events were several M 3.6 and M 3.7 that appeared to occur on the next "ladder rung" to the southeast of the one that broke yesterday in the M 4.8. In this map, yellow events are from yesterday, blue are from today (earlier) and the orange and red are the latest events.
  • hudnut
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Caption: ----------- Overview of the March 24, 2009 M 4.8 earthquake sequence near Bombay Beach, California. Seismicity from 1984-2008 is shown as white symbols (scaled by magnitude; from Lin et al., 2007). The latest events are shown as red circles (precisely re-located as of 3/24/09 noon local time by Egill Hauksson of Caltech). The activity occurred near the intersection of the San Andreas fault and the northeastward projection of the Extra fault zone, near the northern end of the Brawley Seismic Zone. This area has been seismically active previously in Oct. 1999 (Hough and Kanamori, 2002) and Nov. 2001. It has also been noted as being potentially significant for future rupture of the southern San Andreas fault (e.g., Hudnut et al., 1989). Active faults are shown in red if they have ruptured historically (the Elmore Ranch fault zone broke in Nov. 1987, and the Coyote Creek fault broke in 1968). Also shown in orange are faults that have been mapped and that have exhibited triggered creep during regional earthquakes. These include the San Andreas fault and Extra fault zone [data of Susanne U. Janecke, unpublished mapping, Kirby 2005 MS thesis, and Kirby et al. (2007). Additional faults are being mapped.] Other features shown are volcanic centers (orange circles) and various mud pots, carbon dioxide vents (green symbols; from Lynch & Hudnut, 2008). References: ---------------- Hough, S. E., Kanamori, H., Source Properties of Earthquakes near the Salton Sea Triggered by the 16 October 1999 M 7.1 Hector Mine, California, Earthquake Bull. Seis. Soc. Amer., 92: 1281-1289, 2002. Hudnut, K.W., L. Seeber, and J. Pacheco, Cross-fault triggering in the November 1987 Superstition Hills earthquake sequence, southern California, Geophys. Res. Lett., v. 16, No. 2, pp. 199-202, 1989. Kirby, S.M., 2005, The Quaternary tectonic and structural evolution of the San Felipe Hills, California, [M.S. Thesis]: Logan, Utah State University, 182 p. Kirby, S.M., Janecke, S.U., Dorsey, R.J., Housen, B.A., McDougall, K., Langenheim, V., and Steely, A. Jan 2007, Pleistocene Brawley and Ocotillo formations: Evidence for initial strike-slip deformation along the San Felipe and San Jacinto fault zones, California: Journal of Geology, v. 115, p. 43-62. Lin, G., P. Shearer and E. Hauksson (2007), Applying a three-dimensional velocity model, waveform cross correlation, and cluster analysis to locate southern California seismicity from 1981 to 2005, J. Geophys. Res., 112, B12309, doi:10.1029/2007JB004986 Lynch, D. K. and K. W. Hudnut, The Wister Mud Pot Lineament: Southeastward Extension or Abandoned Strand of the San Andreas Fault? Bull. Seis. Soc. Amer., Vol. 98, No. 4, pp. 1720-1729, doi: 10.1785/0120070252, 2008
  • tjordan
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Sally, We've posted the CEPEC statement. We don't intend to release this directly to the media (as far as I know). However, you can use the material freely in your interactions with the media.
  • mcgill
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    I haven't yet received any requests for media interviews, but sometimes I do from newspapers in the Inland Empire. If I am interviewed, is it ok to tell them what is stated above--that CEPEC met this morning and briefed Cal-EMA? I presume that is public information, but thought that perhaps I should check. Sally McGill
  • huynht
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    You can follow the link above (http://scec.usc.edu/eqresponse/?q=node/76) to submit FAQs. Just edit the page and enter content as necessary.
  • arrowsmi
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Many of you know more about this than me, but I was reminded of the similarities with the Superstition Hills and prior events on cross faults in 1987. I am attaching a couple of BSSA papers FYI. Ramon
  • tjordan
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Here's another USGS/Caltech map that includes historical seismicity. This sequence is in red; 2001 is in purple. Note that the current sequence is on bookshelf fault further to the NW, closer to the SAF. Recent activity in red, blue is LSH Imperial Valley DD relocations. red - this sequence purple - LSH IV 2001 blue - LSH IV 1984 - 2002 LSH is Lin, Shearer, Hauksson re-located seismicity plot courtesy of Bob Dollar, USGS
  • marquis
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    Kate Hutton was on KFWB an hour-plus ago talking about this. She might have some pre-prepared comments that would make for a good starting point for an FAQ.
  • minster
    2009.03.24-Bombay Beach Earthquake Sequence   13 years 21 weeks ago
    I get a lot of questions about this swarm. I think it is a good idea to have a set of agreed upon answers, then people can always elaborate. How about contributing to an FAQ list on this? Bernard
  • huynht
    ShakeOut Response Planning - Geology Group   13 years 39 weeks ago
    Mike - What happens when you click on the link "Read more about Field Coordination Plans"? It should take you to another page, which by clicking Edit at the top of the page will allow you to edit as necessary. I tried, but was not able to replicate your error. I checked the settings and they are currently set for edit privileges for everyone.
  • oskin
    ShakeOut Response Planning - Geology Group   13 years 39 weeks ago
    I cannot access the field coordination plans link, above. I would like to be able to add content to that page (in addition to viewing it). One major goal ahead is to pre-define meeting areas for likely rupture scenarios. This web site is a good forum to start this discussion. -Mike
  • jmcguire
    ShakeOut Response Planning - Seismology Group   13 years 39 weeks ago
    I've never looked into the Salton Sea scenario. I think Grahm Kent and the scripps group are looking into putting a lot of instruments in there for the 2010 active source experiment. It might be good to try and get some sort of open rapid response permit worked out after they've figured out what's required. These instruments usually go offshore and can just be deployed, so we don't have any sort of rapid response permitting set up. The pool was setup with the goal of responding to cascadia/aleution/Caribean subduction zone quakes.
  • beroza
    2008.11.13-Great Southern California ShakeOut   13 years 39 weeks ago
    Interesting. We ran into the same issue with the 1906 simulation, as I recall. I suspect that fault width would not have a strong effect, except that it trades off directly with slip at fixed moment, and slip *does* have a strong effect.
  • rloyd
    ShakeOut Response Planning - Geology Group   13 years 39 weeks ago
    The Clearinghouse appreciates all the cooperation from manager and staff of SCEC and the Pasadena USGS office operations. Good show.......
  • rloyd
    ShakeOut Response Planning - Geology Group   13 years 39 weeks ago
    Although the Clearinghouse had been granted a mission number and all necessary approvals from OES to conduct a CAP overflight of the Sierra Madre and northern part of the San Andreas between Lake Hughes and Cajon Pass, CAPs informed us in the past hour that it was too windy to fly so they've aborted the mission.
  • rloyd
    ShakeOut Response Planning - Geodesy Group   13 years 39 weeks ago
    But will be winding down soon........RCL
  • tjordan
    ShakeOut Response Planning - Geodesy Group   13 years 39 weeks ago
    The SCEC facilities at USC remain operational after the Sierra Madre aftershock. Jordan and Hunyh are available.
  • blume
    ShakeOut Response Planning - Geodesy Group   13 years 39 weeks ago
    [simulation] UNAVCO is responding to a request from SCEC on behalf of six SCEC-affiliated institutions: USGS UC Berkeley UC Riverside Harvey Mudd Arizona State Caltech 5 UNAVCO trucks are leaving Boulder as I type to deliver 25 campaign GPS systems to Indio, to arrive early Saturday afternoon at the pre-arranged meeting place. We are preparing an additional 20 systems for Rick Bennett to occupy points in the ECSZ in Joshua Tree N.P. early next week. Preliminary funding authorization has been procured from NSF-EAR and EarthScope by SCEC and UNAVCO directors. [/simulation]
  • beroza
    2008.11.13-Great Southern California ShakeOut   13 years 39 weeks ago
    Nice work! Should be comparing the Mw 7.89 CyberShake ERF34 36_3_0 with the "Real Scenario"? If so, the pattern is extremely similar, but the CyberShake PGVs are lower by as much as ~50%, but never higher. Do you understand why?
  • Treiman
    2008.11.13-Great Southern California ShakeOut   13 years 39 weeks ago
    Just a quick cross-post to refer people in this Recent Earthquakes area to my post on a virtual overflight that can be read in the Geology Coordination area